A brushless motor is used as a driving source of an actuator for controlling exhaust gas, such as an EGR (Exhaust Gas Recirculation) valve, VG (Variable Geometric) turbo-actuator and the like for a vehicle. FIG. 18 is a diagram showing configurations for controlling driving of a brushless motor. In the configuration shown in FIG. 18(a), an ECU (Engine Control Unit) has a function of directly driving a 3-phase brushless motor and the ECU is connected to the brushless motor via a wire harness (ECU direct drive model). The ECU detects the rotational position of the rotor from output signals of Hall ICs acquired from the brushless motor side via the wire harness, and controls driving of the brushless motor in such a manner that the rotational position of the motor agrees with the target position.
In addition, the configuration of FIG. 18(b) comprises an EDU (Electrical actuator Drive Unit) as a dedicated circuit for driving a 3-phase brushless motor. The EDU is connected to the brushless motor via a wire harness, and to the ECU via a CAN (Controller Area Network) (driving circuit separate model). Hall sensor signals are transmitted from the brushless motor side to the ECU via the wire harness and CAN. The ECU supplies the EDU with a control signal according to the rotational position of the rotor detected from the output signals of the Hall ICs, and the EDU controls driving of the brushless motor in accordance with the control signal from the ECU.
In the configuration of FIG. 18(c), a 3-phase brushless motor has a built-in driving circuit, and the ECU is connected to the driving circuit of the brushless motor via a CAN without via a wire harness (driving circuit integrated model). The ECU receives the output signals of the Hall ICs from the brushless motors via the CAN, detects the rotor rotational position, and controls driving of the brushless motor in such a manner that the rotor comes to a target position.
As for the configurations of the ECU direct drive model and driving circuit separate model, they differ from the driving circuit integrated model in that the output signals of the Hall ICs are transmitted to the ECU via the wire harness. Accordingly, if the wire harness has a short circuit or instantaneous interruption or if noise is superposed on a signal passing through the wire harness, there is a possibility that an abnormality occurs on the output signals of the Hall ICs, and that the rotor of the brushless motor shifts from the target position and the motor makes counterrotation. For example, when using a brushless motor as a driving source of an actuator for controlling an EGR valve, and if the foregoing positional shift or motor counterrotation occurs, there is a risk that the components of the motor and valve may be damaged because of a collision of a motor shaft to a motor stopper (open end or closed end).
As a conventional technique for detecting such an abnormality of a brushless motor, there is an abnormality detecting apparatus disclosed in Patent Document 1. The apparatus stores normal output patterns of a magnetic pole position sensor (Hall ICs, for example), which alter in accordance with the rotation of a brushless motor, and makes a decision of an abnormality if the output pattern of the magnetic pole position sensor actually detected deviates from those stored in advance. More specifically, it handles the output signals of the 3-phase (UVW) magnetic pole position sensor as a binary number with the U phase being the upper position and the W phase being the lowest position, and compares the output patterns of the six values the 3-bit data takes in the normal case with the output pattern obtained from the actual signal.
However, the Patent Document 1 makes the abnormality decision only according to the difference from the output patterns in the normal mode. Accordingly, it has a problem of being unable to make a decision as to whether an instantaneous ground short or open on an output signal line of the sensor is a significant abnormality affecting the driving control of the brushless motor or not. For example, even if the instantaneous ground short or open causes a change in the sensor output patterns, there are some cases where the abnormality recovers immediately from the ground short or open, and the shift of the motor from the target position does not occur. Even in such cases, the Patent Document 1 stops the motor in accordance with the difference from the output patterns in the normal mode.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide a motor controller capable of detecting an abnormality accurately and quickly which occurs on an output signal line of a position detecting unit for detecting the magnetic pole position of a rotor and which will have significant effect on the driving of a brushless motor. Another object of the present invention is to provide a motor controller capable of detecting counterrotation of the motor due to the abnormality on the signal line, and capable of correcting driving to the normal rotation direction.